The purpose of the present study was to evaluate the effects of long distance running on bone metabolism, using the biochemical markers ICTP (the carboxyterminal cross‐linked telopeptide of type I collagen), PICP (the carboxyterminal propeptide of type I procollagen), osteocalcin and bALP (bone specific alkaline phosphatase) as well as parathyroid hormone (PTH) and serum calcium. Twenty healthy, regularly exercising individuals, 10 women and 10 men, participated in a running competition. The mean age was 38 (range 22–55) and 39 (range 22–53) years respectively, the performed distance 15 (range 5–30) and 28 (range 15–30) km respectively, with a speed of 5:30, 5:02 per kilometer respectively. Fasting blood samples were drawn in the morning the day before the race, and also the day after and two days after. A decrease of PICP concentrations among women was evident the day after the competition (from 170±17 μ/l to 158±17 μg/l) which returned to pre‐exercise levels two days after the race (167±19 μg/l). Furthermore, a decrease of osteocalcin could be seen in the men one day after the exercise (from 12.1± 1.1 μg/l to 10.3±1.1 μg/l). In the men, there was also an increase of ICTP concentrations two days after (3.98±0.35 μg/l) this long‐term and demanding exercise, when compared with pre‐exercise levels (3.67±0.28). One single bout of longterm, exhaustive running exercise in well‐trained men and women seems to induce a temporary inhibition of bone formation as well as a